Flow conditioners have been known for quite some time and serve to convert a flow into a flow with a known flow profile. Compare, for example, U.S. Pat. Nos. 3,840,051, 5,341,848, DE 10 2006 046 252 A1 and U.S. Pat. No. 5,529,093. Known forms of embodiment are also discussed in the paper, “A new concept of flow conditioner under test”, by B. Mickan, G. Pereira, J. Wu and D. Dopheide.
Developing these ideas, DE 10 2011 079 933 A1 discloses a flow conditioner with holes on concentric circular paths, which get larger toward the center.